Paper shredder

ABSTRACT

A shredding apparatus for paper and the like is defined by a pair of spaced, parallel counterrotating rolls provided with spaced-apart, cylindrical and overlapping shredding discs. The discs do not come into contact, for friction-free operation of the shredder and have sharp corners and a high friction surface finish for engaging inserted paper. The paper is stretched and thereby torn or shredded as it is engaged by the discs and passes between the rolls.

D United States Patent [111 3,630,460

[72] Inventor Albert Goldhammer l 56] ma m m s? PM UNITED STATES PATENTSMy 221,744 11/1879 Sanford 241 /236 x [211 App]. No. 867,664

313,987 3/1885 Burckhardt. 241/236 X [22] Filed Oct, 20, 1969 2,236,9694/1941 Flateboe 241/236 X [45] Patented Dec. 28, 1971 [32] pfiomy mm,1968 3,190,573 6/1965 B ehn 241/236 [33] may 3,396,914 8/1968 L1ebman241/236 X [3]] P 18 08 155.5 3,502,276 3/1970 Panning... 241/236 X 33,529,782 9/1970 Liebman 241/236 Primary Examiner- Donald G. KellyAtt0mey- Edward Brosler ABSTRACT: A shredding apparatus for paper andthe like is l 54] PAPER SHREDDER defined b a pair of spaced, parallelcounterrotating rolls pro- 8 Chi- 3 m vided with spaced-apart,cylindrical and overlapping Ill shredding discs. The discs do not comeinto contact, for fric- [52] US. 241/236 tion-free operation of theshredder and have sharp corners [51] Int. C 80% 4/08, and a highfriction surface finish for engaging inserted paper.

B02c 4/30 The paper is stretched and thereby torn or shredded as it isen- [50] Field of Search 241/236 gaged by the discs and passes betweenthe rolls.

Patented Dec. 28, 1971 3,630,460

INVENTORI- A 5537 60LOH/4MMER Attorney PAPER SHREDDER The presentinvention relates to a shredding apparatus for material such as paperand more particularly to a shredder provided with counter rotating rollshaving opposing, counterrotating and overlapping annular rings.

Shredders having parallel shredding rolls fitted with overlapping, sawtooth-shaped external threads are known (British Pat. No. 1,002,799).The threads are fonned with outwardly arching side faces that terminatein relatively sharp but rounded ridges. The rolls are positioned so thatthe threads are disposed in the corresponding grooves of the oppositeroll. Substantial clearance is maintained between the side faces of theoverlapping roll threads. To facilitate the grasping of paper and itsautomatic transportation through the shredder the thread ridges have acoarse surface finish or are coated with a high-friction material.

In use, such shredders have exhibited a low capacity and functionpoorly. The saw tooth-shaped thread profile provides relatively smallcontact areas for the material to be shredded. This causes difiicultiessince the material must be advanced by the rolls. The tear effect, thatis the excessive stretching of the material as it passes through thespace between the rolls, is relatively small even if the opposingthreads overlap a substantial distance because the material is only tornat the thread ridges. However, even that tearing action is not alwaysassured. If the inserted material comprises narrow strips, the stripscan glide over the thread ridges and the material is merely crushedinstead of torn or shredded, thus leading to no more than anintermittent shredding action.

Other known shredders comprise cutting devices which have a pair ofparallel, counter rotating rolls. The rolls are provided withdisc-shaped cutters that have sharp cutting edges in mutual engagement;

Such shredders can only operate when the cutting edges of the opposingdisc cutters contact each other. The cutting edges must be sharp for atrouble-free operation. It is further necessary that the width of spacesbetween the disc cutters is closely controlled and equal to thethickness of the discs of the opposing roll entering such spaces.

Paper cutters of the above-outlined design require the highest precisionin their manufacture and are therefore expensive. Such prior art papercutters have another major shortcoming. The tight fit of the cuttingdiscs, a must for their trouble-free operation, develops high frictionin the area of the coacting, opposing cutting edges. Tests have shownthat friction absorbs up to 50 percent of the output power of the drivemotor so that the efiiciency of the shredder is quite low. Additionally,the cutting edges must be frequently sharpened to assure satisfactoryoperation of the shredder.

A prime objective of the present invention is to provide a shredderhaving a high efficiency so that its capacity is substantially greaterthan prior art shredders having a like power input.

A further objective of the invention is to provide a shredder whichsecurely grasps inserted material between its counter rotating rolls andwhich positively shreds the material into narrow strips.

The shredder of this invention has a pair of parallel rolls mountingspaced-apart, cylindrical shredding discs of a square or rectangularcross section. The discs have sharp corners and a thickness that is atthe most one-tenth smaller than the axial spacing or gap-betweenadjacent discs of the opposing roll. The discs extend into that gap adistance about equal to the thickness of the discs.

The shredder of the present invention has the advantage that itstretches inserted material to a much greater extent than prior artshredders having a like overlap of the cutting discs or threads. Forexample, the previously discussed prior art shredders provided with asaw tooth-shaped thread profile stretch the material to about 1.5 timesthe thread overlap. In contrast thereto, the shredding rolls of thepresent invention stretch the material to three times the overlap of theshredding discs.

Additionally, the tear effect is substantially enhanced by the fact thatthe material is simultaneously grasped by four sharp corners at eacheffective disc pair of the rolls. Consequently, slidable movements ofthe inserted material in an axial or the feed through direction of theshredder are prevented by the multiple contact points between thematerial and the shredding discs. To further enhance the engagement ofthe material by the shredding discs, the cylindrical outer surfaces ofthe latter preferably have a coarse surface finish to increase theircoefficient of friction.

A further advantage of the present shredder over prior art shreddersresults from the simultaneous engagement of the inserted material bysharp disc comers and the coarse exterior surfaces of the shreddingdiscs. The transportation of the inserted material in the feed directionand through the shredding rolls is thereby substantially enhanced. Thisin turn increases the capacity of the shredder while its use issimplified. It is presently preferred to form the exterior cylindricalsurfaces of the shredding discs with axially oriented, relatively coarsegrinding or tool marks.

This has a twofold advantage. First, it results in an excellentengagement of the inserted material by the shredding discs and,secondly, it causes sharper shredding disc corners to thereby increasethe tear efficiency of the shredder significantly. It is furtheradvantageous to surface harden the discs by a process such as nitridehardening to reduce their wear.

For highest shredding efficiency and capacity of the shredding apparatusof the invention, it is best to rotate the rolls at a rate providing ashredding disc surface speed of between about 1.1 m. (meter) to about1.75 m. per second.

At the indicated operating speed of the shredder rolls a good feed rateof the inserted material and an excellent tear efficiency is obtained.The shredder exhibits optimum operating characteristics when thefeedthrough speed and intake acceleration of the inserted material havethe values obtained from the above-indicated shredding disc speeds.Furthermore, if paper is being shredded at the above speeds it isdynamically torn where it inhibits reduced strength, as compared to thepapers static strength, to thus reduce the power requirement of theshredder.

In contrast to the above-referred-to prior art paper-cutting device, theshredder of the present invention has a much greater efficiency. In thepresent shredder the shredding discs do not come into contact, as is thecase with that prior art device Energy dissipation due to a frictionalengagement of the shredding discs is thus eliminated and virtually thetotal power input is available for the actual shredding of the insertedmaterial.

The invention is further described in connection with the accompanyingdrawings and the therein illustrated embodiments from which additionalfeatures and advantages of the invention are apparent.

FIG. 1 is a fragmentary plan view of a pair of parallel shredding rollsconstructed in accordance with the present invention;

FIG. 2 is a fragmentary view similar to FIG. 1 and illustrates anotherembodiment of the invention; and

FIG. 3 is an elevational view, in section, and is taken on line A-B ofFIG. 1.

Referring to FIG. 1, the first illustrated embodiment of the shredder ofthe present invention comprises a pair of parallel, nonidentical rolls 1and 2. The rolls have cores 3 and 4, respectively, from which aplurality of discs 5 and 6, respectively, extend. The axial spacing a2between adjacent discs 6 of roll 2 equals the thickness d2 of the discs.The axial spacing a2 between adjacent discs 5 of roll 1, on the otherhand, exceeds the thickness of opposing discs 6 of roll 2 so that thethickness dl of discs 5 is less than the thickness d2 of discs 6.

This arrangement of the discs and rolls enables the discs to overlapeach other. Discs 5 of roll I extend into gaps 7 defined by discs 6 ofroll 2. Likewise, discs 6 of roll 2 extend into gaps 8 defined by discs5 of roll 1. The magnitude of the overlap corresponds to about thethickness d2 of discs 6 of roll 2.

The difference in the thickness of discs 5 and the axial spacing a2between discs 6 of roll 2, and the difference in the thickness d1 andthe axial spacing a1 between discs 5 result in an axial spacing ornarrow gaps 9 and 10 between adjacent discs 5 and 6 in the disc overlapregion generally identified with e. There is thus no contact betweendiscs 5 and 6 of rolls 1 and 2 and, during operation of the shredder, noenergy losses from friction between the discs are encountered.

The thickness of gaps 9 and 10 is between 0.05 mm. (millimeters) andabout 0.25 mm. Discs 6 of roll 2 have a thickness of about 5 to 6millimeters.

As best seen in FIG. 3, discs 5 and 6 have a cylindrical configuration.Cylindrical surfaces II and 12 and annular faces 13, 14 and I5, 16,respectively, of discs 5 and 6 further define sharp circular edges 17,I8 and 19, 20, respectively.

The cylindrical surfaces 11 and 12 of discs 5 and 6 are coarselymachined. The coarse surface finish is preferably obtained from tool orgrinding marks which extend in an axial direction to increase thecoefficient of friction of cylindrical surfaces 11 and 12. T reduce thedanger of damage to the finish of disc surfaces 11 through 16 andparticularly to sharp edges 17 through 20 from accidental contact withhard foreign objects the surfaces of the discs are surface hardened.

The diameters of cores 3 and 4 and of discs and 6 are identical. Thediameters and the spacing of the axes of rolls 1 and 2 is selected sothat the distance between the exterior rolls surfaces equals the overlape plus 2s. Passageways 21 and 22 of equal widths s remain between discs5 and 6 and cores 4 and 3, respectively.

In the embodiment illustrated in FIG. 1 the thicknesses d1 and d2 ofdiscs 5 and 6 and the axial spacings a1 and a2 between adjacent discs 5and 6 differ. Referring now to FIG. 2, in another preferred embodimentof the invention, rolls 1 and 2' are provided with discs 5' and 6,respectively, which have equal thicknesses d. The axial spacings betweendiscs 5 and 6 are also equal. In this embodiment of the invention thethickness d of discs 5 and 6 is between 0.1 mm. and about 0.5 mm. lessthan the spacing a between adjacent discs 5 and 6'. Narrow axial gap 9and therefore exist between adjacent discs 5' and 6' in the overlapregion of the discs and direct contact between discs 5' and 6' of rolls1' and 2 is prevented.

In the embodiment of the shredder illustrated in FIG. 1 rolls 1 and 2are nonidentical since the disc thicknesses d1 and d2 and the axial discspacings a1 and a2 of discs 5 and 6 differ. In the embodimentillustrated in FIG. 2, however, rolls 1 and 2 are identical. Forpractical considerations the embodiment illustrated in FIG. 2 istherefore presently preferred.

Discs 5' and 6 are also cylindrical. The discs also include exteriorcylindrical surfaces 11 and 12 and sharp comers l7, l8 and 19, 20. Thecylindrical surfaces 11 and 12 are provided with a coarse surface finishand discs 5' and 6 are surface hardened as previously described.

In operation rolls 1 and 2 or 1 and 2' are driven in opposing directionsas indicated by arrows 23 and 24 at a rate so that the cylindricalsurfaces of discs 5, 6 or 5', 6', have a speed of between about 1.1 andabout 1.75 meters per second. Materials, e.g. paper to be shredded, isinserted from above between the rolls in the direction of arrow 25.

Referring now to FIG. 3, corners 17, 18 (or cylindrical surface 11) ofdiscs 5 or 5 and comers 19, (or cylindrical surface 12) of discs 6 or 6'intersect at point 26 at an acute angle. The magnitude of that angle hasa significant influence on the effectiveness with which rolls 1 and 2 or1' and 2' pull in the material inserted in the direction of arrow 25.The effectiveness increases with a decrease of the angle defined byexterior surfaces 11 and 12 of discs 5, 6 or 5, 6'. The magnitude of theangle is a function of both the overlap e and the diameter of discs5,6or5,6.

The above-described prior art paper-cutting devices can be provided witha relatively small overlap e that may have a minimum which equals thethickness of the inserted material. However, shredders of the typedisclosed herein require an overlap e which is substantially greaterthan the permissable minimum for such prior art cutting devices. Thegreater overlap is necessary because the overlap determines the extentto which the inserted material is stretched and, therefore, itdetermines the effectiveness with which the paper is torn. Since papershredders are generally relatively small office appliances, the increaseof overlap e through an increase in the diameter of discs 5, 6 or 5, 6'is limited by overall size considerations. Determination of the greatestpossible overlap e for maximum shredding effectiveness, anddetermination of the minimum angle between exterior cylindrical surfaces11 and 12 at their intersection 26 for maximum pull-in effectivenesstherefore require an optimization of these two parameters.

It has been established that best results are obtained when overlap e isbetween about one-seventh to one-tenth the diameter ofdiscs 5, 6 or 5',6'.

The coarse, high-friction surfaces 11 and 12 of discs 5, 6 or 5', 6grasp inserted material at intersection 26 and thereafter pull itthrough between rolls 1 and 2. Sharp corners 17, 18 and 19, 20,respectively, of discs 5, 6 or S, 6' prevent movement in the axialdirection of the rolls of paper being pulled through the shredder. Atthe same time the inserted material, say paper, is stretched to amultiple of its possible elastic elongation by an amount equal tooverlap e so that it is tomor shredded.

In contrast to prior art cutting devices of the type discussed above,there is no friction between the moving components of the shredder ofthe present invention with the exception of negligible friction in thebearings (not shown) of rolls 1, 2 or 1', 2. This enables the use ofalmost the full input power for the shredding of the inserted materialto give the shredder an excellent efficiency. Trouble-free operation ofthe shredder is assured by construction discs 5, 6 or 5', or 6 and bydetermining the extent of overlap e as described in the precedingparagraphs.

Iclaim:

1. Apparatus for shredding tearable material comprising a pair ofshredding rolls, each including a plurality of axially spaced ribsforming troughs therebetween, with ribs of each roll meshing with ribsof the other roll in axial spaced relationship thereto and with each ofsaid ribs having a sharp edge at each side, whereby to grip saidtearable material when passing between said rolls as said ribs pull saidtearable material into said troughs to effect tearing of such materialalong said sharp edges.

2. Apparatusin accordance with claim 1, characterized by each of saidribs having substantially parallel side surfaces and substantiallycylindrical surface connecting with said side surfaces in sharp edges.

3. Apparatus in accordance with claim 2, characterized by thesubstantially cylindrical surface of each of said ribs having axiallydirected markings therein, whereby to increase the grip of said ribs ontearable material passing between said rolls, while said ribs pull saidtearable material into said troughs to effect tearing along said sharpedges.

4. Apparatus in accordance with claim 2, characterized by a spacingbetween each of said ribs and the proximate walls of its associatedtrough being of the order of 0.050.25 mm.

5. Apparatus in accordance with claim 4, characterized by each of saidribs on its cylindrical surface, having axially directed markingstherein, whereby to increase the grip of said ribs on tearable materialpassing between said rolls, while said ribs pull said tearable materialinto said troughs to effect tearing along said sharp edges.

6. Apparatus in accordance with claim 3, characterized by means forrotating said rolls in opposite directions and at like speeds.

7. Apparatus in accordance with claim 6, characterized by I the speed onthe cylindrical surfaces of said ribs being of the order of 1.1- l .75meters per second.

8. Apparatus in accordance with claim 3 characterized by a spacingbetween each of said ribs and the proximate walls of its associatedtrough being of the order of 0.05-l.75mm., and

means for rotating said rolls in opposite directions with a speed on thecylindrical surfaces of said ribs of the order of 1.1-1.75 meters persecond.

1. Apparatus for shredding tearable material comprising a pair ofshredding rolls, each including a plurality of axially spaced ribsforming troughs therebetween, with ribs of each roll meshing with ribsof the other roll in axial spaced relationship thereto and with each ofsaid ribs having a sharp edge at each side, whereby to grip saidtearable material when passing between said rolls as said ribs pull saidtearable material into said troughs to effect tearing of such materialalong said sharp edges.
 2. Apparatus in accordance with claim 1,characterized by each of said ribs having substantially parallel sidesurfaces and substantially cylindrical surface connecting with said sidesurfaces in sharp edges.
 3. Apparatus in accordance with claim 2,characterized by the substantially cylindrical surface of each of saidribs having axially directed markings therein, whereby to increase thegrip of said ribs on tearable material passing between said rolls, whilesaid ribs pull said tearable material into said troughs to effecttearing along said sharp edges.
 4. Apparatus in accordance with claim 2,characterized by a spacing between each of said ribs and the proximatewalls of its associated trough being of the order of 0.05-0.25 mm. 5.Apparatus in accordance with claim 4, characterized by each of said ribson its cylindrical surface, having axially directed markings therein,whereby to increase the grip of said ribs on tearable material passingbetween said rolls, while said ribs pull said tearable material intosaid troughs to effect tearing along said sharp edges.
 6. Apparatus inaccordance with claim 3, characterized by means for rotating said rollsin opposite directions and at like speeds.
 7. Apparatus in accordancewith claim 6, characterized by the speed on the cylindrical surfaces ofsaid ribs being of the order of 1.1-1.75 meters per second.
 8. Apparatusin accordance with claim 3 characterized by a spacing between each ofsaid ribs and the proximate walls of its associated trough being of theorder of 0.05-1.75mm., and means for rotating said rolls in oppositedirections with a speed on the cylindrical surfaces of said ribs of theorder of 1.1-1.75 meters per second.